Relation Between the Deletion Polymorphism of the Angiotensin-Converting Enzyme Gene and Late Luminal Narrowing After Coronary Angioplasty
Background The insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene has been implicated in the pathogenesis of coronary artery disease. The deletion allele is strongly associated with the level of circulating ACE and is a potent risk factor for myocardial infarction. Recently, the deletion allele was also associated with the occurrence of visually diagnosed restenosis after percutaneous transluminal coronary angioplasty (PTCA) in a selected population of patients with acute myocardial infarction.
Methods and Results We investigated the influence of the ACE I/D polymorphism on the occurrence of restenosis after PTCA with the use of quantitative coronary angiography. ACE I/D genotypes were characterized in 118 consecutive patients who had one-vessel disease and were undergoing systematic angiographic follow-up. Coronary angiograms were analyzed before and after PTCA and at follow-up (7.4±3.0 months). Before PTCA, there were no clinical or angiographic differences among the three groups of genotypes (DD, n=39; ID, n=62; II, n=17). After PTCA, the mean differences in minimal luminal diameter between post-PTCA and pre-PTCA angiograms (acute gain) were identical in the three groups, as was the mean percent residual stenosis. At follow-up angiography, the mean difference in minimal coronary luminal diameter between post-PTCA and follow-up angiograms (late loss) was not significantly different in the three groups of genotypes. The percentage of patients with restenosis defined as a >50% stenosis was identical in the three groups.
Conclusions In this quantitative study, the I/D polymorphism of the ACE gene had no influence on the occurrence of restenosis after coronary angioplasty.
Recurrent narrowing of treated coronary artery after initially successful percutaneous transluminal coronary angioplasty (PTCA) is a major limitation of this method of myocardial revascularization.1 The identification of risk factors for restenosis could help to prevent and reduce the impact of this phenomenon. Experimental studies support the hypothesis that the renin–angiotensin system plays a major role in the pathogenesis of restenosis; in animal models, the renin–angiotensin system is implicated in the arterial response that follows angioplasty,2 3 and angiotensin I–converting enzyme (ACE) inhibitors prevent neointimal thickening after balloon denudation.4 The plasma and cellular levels of ACE are associated with an insertion/deletion (I/D) polymorphism in the ACE gene, and the presence of the D allele of the ACE gene is associated with higher levels of plasma ACE.5 6 7 This allele is also a risk factor for myocardial infarction.8 Recently, the presence of the D allele was found to be a potent risk factor for qualitatively assessed restenosis after angioplasty of the infarct-related vessel.9
To assess the impact of the D allele of the ACE gene as a restenosis risk factor, we estimated with quantitative angiography the occurrence of restenosis in a series of 118 patients with one-vessel disease who underwent a successful angioplasty procedure.
In a routine follow-up program of cardiac catheterization after PTCA, we recruited 118 consecutive patients with one-vessel disease who had previously undergone a successful angioplasty procedure. Angioplasty was performed according to the standard technique in our laboratory, as previously described.10 The procedure was considered successful when the residual luminal narrowing in the dilated segment, immediately after angioplasty, was estimated visually to be <50% and when no major complication (ECG or enzymatic evidence of myocardial infarction, need for bypass surgery during hospitalization, or in-hospital death) occurred. Angiography was performed in at least two projections, after the intracoronary injection of isosorbide dinitrate (2 mg), just before and immediately after angioplasty. These projections were recorded in our database, and the follow-up angiogram was performed, after the intracoronary injection of isosorbide dinitrate, in the same projections.
Qualitative Angiographic Analyses
The qualitative analyses were performed independently by two experienced interventional cardiologists. Disagreements were resolved by an additional joint reading. Lesions were classified as concentric (symmetric narrowing, with an identical or almost identical appearance in orthogonal projections) or eccentric (asymmetric narrowing, with the stenotic lumen appearing to lie within the outer half of the “normal” lumen of the vessel in at least one projection). The presence of calcification or thrombus (a discrete intraluminal filling defect) was also noted. The anterograde blood flow before angioplasty was graded using the classification of the Thrombolysis in Myocardial Infarction (TIMI) Study group.11 Lesions were classified in accordance with the American Heart Association/American College of Cardiology (AHA/ACC) classification as modified by Ellis et al.12
Quantitative Coronary Angiography
Quantitative computer-assisted angiographic measurements of the dilated lesion were performed on angiograms obtained just before angioplasty, immediately after angioplasty, and at follow-up. Measurements were performed on end-diastolic frames with use of the CAESAR (Computer-Assisted Evaluation of Stenosis and Restenosis) system. The 35-mm cinefilm was projected with a 35AX projector, and the cine frame selected for analysis was scanned with a high-resolution (matrix, 1024×1024 pixels) video camera. The signal produced by the video camera was digitized and displayed on a video monitor. Regions of interest were chosen in the vessel, and a centerline was traced manually with a light pencil. The diameter of the coronary catheter was used to convert the imaging data from pixels to millimeters. The mean diameters of proximal and distal reference segments and the minimum diameter of the stenotic segment were measured. We have previously determined the accuracy and the precision of the CAESAR system.13
Serum Lipid and Lipoprotein Analysis
At follow-up, serum total cholesterol and triglyceride levels were measured by enzymatic methods (Boehringer Mannheim FRG). Cholesterol was measured in the HDL-containing supernatant after sodium phosphotungstate/magnesium chloride precipitation (Boehringer Mannheim FRG). An estimate of the LDL-cholesterol was computed according to Friedewald’s formula. Apolipoproteins AI and B were quantified by the use of immunonephelometry (Behringwerke).
At follow-up, venous blood samples were collected in Vacutainer tubes containing EDTA anticoagulant. Genomic DNA was prepared from white blood cells as previously described.14 The ACE gene fragment containing sequence was amplified with a Perkin-Elmer DNA thermal cycler and Thermus aquaticus DNA polymerase (Amersham) with the use of the primer sequences previously described.15 Reaction products were analyzed on agarose gel for allele identification.
Statistical analyses were performed with sas software, version 6.08 (SAS Institute Inc). Mean and SD values of quantitative data were calculated. Quantitative data were compared with a general linear model according to the ACE genotypes (ie, DD, ID, II). Qualitative data were tested with the use of Pearson’s χ2 test.
Most of the 118 patients were smokers (72%). The mean serum LDL-cholesterol level was 123±31 mg/dL, and the mean serum HDL-cholesterol level was 43±12 mg/dL. A family history of coronary artery disease was observed in 38% of the patients. The overall population had good left ventricular function (mean ejection fraction, 0.62±0.14). One third of the patients had PTCA for unstable angina, and a similar proportion had experienced an acute myocardial infarction in the month before PTCA. Of the 118 patients, 39 had the DD genotype (33%), 62 had the ID genotype (53%), and 17 had the II genotype (14%). These genotype frequencies were compatible with the Hardy-Weinberg distribution. The clinical characteristics for the three groups of genotypes are presented in Table 1⇓. Except for age, which was higher in the ID patients, there were no statistically significant differences among genotypes.
The angiographic characteristics of the dilated lesions are summarized in Table 2⇓. Most of the lesions were located in the left anterior descending or right coronary artery and were classified as type A or B1 according to the ACC/AHA classification modified by Ellis et al12 ; the majority of the stenoses were in arteries that had TIMI grade 3 flow. All the angiographic characteristics were similar among the three groups of genotypes.
The follow-up period (from PTCA to follow-up angiogram) was 7.4±3.0 months for the overall population and did not differ significantly among groups (DD, 7.6±4.0 months; ID, 7.4±2.5 months; II, 7.1±1.8 months). The medications taken by the patients during this follow-up period were similar for the three groups; 21% of the patients were treated with an ACE inhibitor (DD, 20%; ID, 23%; II, 18%).
The results of quantitative coronary angiography did not show any differences among groups in reference diameter, minimal luminal diameter, or percent diameter stenosis before angioplasty (Table 3⇓). Immediately after the PTCA procedure, the minimal luminal diameter, percent diameter stenosis, and amount of acute gain were similar in the three genotypes. At follow-up angiography, the minimal luminal diameter, percent diameter stenosis, and late loss were not statistically different in the three groups of genotypes. Finally, when restenosis was categorized from the quantitative data and defined as a >50% stenosis at follow-up, no differences in the percentages of restenosis were observed among the three genotypes. At follow-up, the proportion of patients with total occlusion was similar in the three groups of genotypes. When the patients with total occlusion were excluded, the late loss again was not statistically different in the three groups of genotypes (DD, 0.35±0.70 mm; ID, 0.39±0.53 mm; II, 0.31±0.58 mm).
In this quantitative study, the deletion polymorphism of the ACE gene had no influence on the occurrence of restenosis after coronary angioplasty. No significant differences were observed for any of the confounding factors tested. Regardless of the criterion used for assessing restenosis at follow-up (eg, minimal luminal diameter, percent stenosis, late loss, net gain, presence of a >50% diameter stenosis), no differences were observed among the three genotypes. These results suggest that the D allele of the ACE gene is not a major risk factor for restenosis after PTCA. Contrary to the observation reported by Ohishi et al9 in a smaller sample, the incidence of restenosis in the present study was similar for the three genotypes. Several explanations may account for this discrepancy. First, the 82 consecutive patients in the study of Ohishi et al9 had visual assessment of restenosis performed, which was arbitrarily defined as a >50% stenosis at follow-up; the shortcomings associated with visual analysis of coronary angiograms are now universally recognized, and the use of quantitative angiography allows better accuracy and reproducibility.13 Second, Ohishi et al9 included only patients who had emergency PTCA for an acute myocardial infarction; PTCA in this setting has been associated with a significant proportion of reocclusion,16 which is less frequently observed after elective PTCA.17
When we compared the genotypic and allelic distributions in the present study population with the results obtained in the ECTIM study8 and the study of Ohishi et al9 (Table 4⇓), the distributions of genotypes and alleles in the patients with myocardial infarction in the ECTIM study and in our patients were comparable. In contrast, Ohishi et al9 found a higher frequency of D alleles due to the lower frequency of ID genotypes. Moreover, due to this deficit in heterozygotes, the genotype distribution was not compatible with the Hardy-Weinberg equilibrium (P<.05). This heterozygote deficit may be related to ethnic differences or to amplification confusion between ID and DD genotypes, as previously described.18
Although the relative contributions of the mechanisms leading to restenosis after PTCA in humans are not yet fully determined,1 experimental and clinical studies have demonstrated the importance of neointimal hyperplasia.19 There are numerous experimental observations suggesting that an inhibition of ACE reduces neointimal hyperplasia in response to experimental balloon angioplasty.4 20 Potential mechanisms by which ACE inhibition may reduce neointimal hyperplasia in these models are related to the role of this enzyme in the formation of angiotensin II, a potent growth factor for smooth muscle cells,21 and in the degradation of bradykinin, a growth inhibitor for smooth muscle cells.22 However, two recent randomized trials (MERCATOR23 and MARCATOR24 ) failed to demonstrate a beneficial effect of ACE inhibition on the occurrence of angiographic restenosis after angioplasty in humans. One potential explanation for these discrepancies might be the relatively low doses of ACE inhibitor used in the clinical trials compared with the experimental studies, which were unable to achieve a significant inhibition of tissue ACE.20 In humans, the levels of plasma and cellular ACE are strongly genetically determined5 6 25 ; the DD genotype is associated with a higher level of ACE than either the ID or II genotype.5 Based on these studies, we hypothesized that the DD genotype might be a risk factor for restenosis after a successful angioplasty procedure. Our results suggested that such an effect, if any, was unlikely to be of major clinical significance or that an interaction with other genes or environmental risk factors could mask this association. A limitation of the present study relates to the number of patients included. However, given the strength of the relation described by Ohishi et al9 in a smaller group, one would expect to see significant differences among the groups in a sample of this size.
This work was supported in part by a grant from the Direction de la Recherche et des Etudes Doctorales and Institut Pasteur de Lille. We thank Thierry Brousseau and Odile Vidal for their excellent assistance.
- Received November 8, 1994.
- Revision received January 23, 1995.
- Accepted January 30, 1995.
- Copyright © 1995 by American Heart Association
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